Nitric oxide radical reactions

This statement does not mean, however, that the mechanism of diazotization was completely elucidated with that breakthrough. More recently it was possible to test the hypothesis that, in the reaction between the nitrosyl ion and an aromatic amine, a radical cation and the nitric oxide radical (NO ) are first formed by a one-electron transfer from the amine to NO+. Stability considerations imply that such a primary step is feasible, because NO is a stable radical and an aromatic amine will form a radical cation relatively easily, especially if electron-donating substituents are present. As discussed briefly in Section 2.6, Morkovnik et al. (1988) found that the radical cations of 4-dimethylamino- and 4-7V-morpholinoaniline form the corresponding diazonium ions with the nitric oxide radical (Scheme 2-39). 

Nitramines are known to photodissociate from their jt,jt state to give aminyl and nitric oxide radicals in the presence of an acid the aminyl radicals are protonated to give aminium radicals, which can initiate addition to olefins. As a synthetic reaction, photolysis of nitramines in the presence of acids can be conveniently run under oxygen to give oxidative addition similar to those shown in equation 145 indeed TV-nitrodimethylamine is photolysed with triene 299 under such conditions to give a mixture of 301 and 302, similar to results observed in the oxidative nitrosamine photoaddition169. To simplify the isolation, the crude products are reduced with LAH to form the open-chain amino alcohol 303. Some other oxidative photoadditions of N-nitro dimethylamine to other olefins are reported. As the photoreaction has to use a Corex filter and product yields are no better than those shown by nitrosamines, further investigations were scarcely carried out. 

The primary process following a photoexcitation of nltrosamldes XIV Is the dissociation of the N-N bond to form a radical pair XV and the ensuing chemical events are the reactions of amldyl and nitric oxide radicals In the paired state or Individually In the bulk of solutions. Naturally, secondary reactions, thermal or photolytic, have to be taken Into consideration under Irradiation conditions (21). First of all, the relatively straightforward chemistry of selective excitation In the n-ir transition band (>400 nm) will be discussed, followed by the chemistry of Irradiation with a Pyrex filter (>280 nm). As nitric oxide Is known to be rather unreactlve (23), primary chemical processes In the Irradiation with >400 nm light under... 

Four routes to form peroxynitrite from nitric oxide. The reaction of nitric oxide with superoxide is only one mechanism leading to the formation of peroxynitrite. Supetoxide could also reduce the nitrosyidioxyl radical. If nitric oxide is directly reduced to nitroxyl anion, it will react with molecular oxygen to form peroxynitrite. At acidic pH, nitrite may form nitrous acid and nitrosonium ion, which reacts with hydrogen peroxide to form peroxynitrite. 

At low concentrations of chlorine, dimeric nitrosoalkanes free from chlorine are produced when alkanes are treated also with nitric oxide. Under these circumstances, molecular chlorine is first converted into atomic chlorine which attacks the alkane to form alkyl radicals and hydrogen chloride. The alkyl radicals, in turn, form nitrosoalkanes with nitric oxide. This reaction is most effectively carried out when the ultraviolet radiation is between 380 and 420 mp. [43, 56],... 

The reaction of alkenes with nitric oxide (NO), a mixture of nitric oxide and oxygen, or dinitrogen trioxide leads to /i-nitroso nitro compounds ( / -nitrosites or pseudo-nitrosites), which can convert to nitroso dimers79. Nitroalkenes are common byproducts in these reactions. The formation of /i-nitroso nitro compounds in the reaction between alkenes and nitric oxide is explained by the presence of nitrogen dioxide and dinitrogen trioxide in the nitric oxide. The reaction may be initiated by the attack of the N02 radical on the alkene to give a /i-nitroalkyl radical which then couples with nitric oxide. 

Simeonova and Luster 1995). Reduction of TNF-a in vivo results in a protection from asbestos-induced fibrotic changes (Brass et al. 1999 Liu et al. 1998). Some of the asbestos-induced inflammatory reactions may be related to fiber type. For example, crocidolite, but not chrysotile, induced increased production of TNF-a and interleukin 1(3 in cultured rat alveolar macrophages exposed for up to 14 days, whereas chrysotile, but not crocidolite, increased production of superoxide anion and nitric oxide radicals (Mongan et al. 2000). 

The reaction of phenols with nitrous acid gives the ortho- and para-nitroso products, which are formed through a neutral dienone intermediate, the proton loss from the latter being the rate-limiting step" " . It has been shown that the nitrous acid can act as a catalyst for the formation of the nitro derivatives. Thus the conventional preparation of nitro compounds by the oxidation of nitroso compounds may be replaced by methods using an electron-transfer pathway in certain cases. In the latter method, the phenoxide reacts with nitrosonium ion to give the phenoxy radical and nitric oxide radical. The nitric oxide radical is in equilibrium with the nitronium radical by reaction with nitronium ion. The reaction of the phenoxy radical with the nitroninm radical resnlts in the formation of the ortho- and para-mixo prodncts" . Leis and coworkers carried ont kinetic stndies on the reaction of phenolate ions with alkyl nitrites and fonnd that the initially formed product is the 0-nitrite ester, which evolves by a complex mechanism to give the ortho-and the para-nitro products". ... 

L. Packer V. Kagan E. Cadenas, In Antioxidant Activity of Coenzyme Q and Ubiquinols Reactions with Tocopheroxyl and Nitric Oxide Radicals Proceedings ot the First Conterence ot the International Coenzyme Q-10 Association, Boston, MA, USA, 1998, Abstract pp 22-24. 

The second direct reaction pathway, one-electron reduction of a target by nitric oxide, could occur only if the target was itself a strong oxidant, since nitric oxide does not readily give up its unpaired electron. Oxidation of nitric oxide would result in the formation of NO, which would rapidly nitrosate nucleophiles such as amines, sulfhydryls, or aromatics. In fact, the best one-electron oxidants would be radicals such as -NOi or hydroxyl radical or even ONOO itself. In such cases the net effect would be nitric oxide addition reactions (nitrosations), regardless of whether the mechanism is considered to be transfer of an electron from nitric oxide followed by attack of NO or simple radical-radical combination. Thus, under most conditions, one-electron reduction of a target by nitric oxide becomes a simple addition reaction. 

Nitric oxide radicals (ti/2 about 2-3years) destroy ozone in a catalytic process. In the stratosphere, they also stem from emissions from planes and rockets, and reactions of N2O with... 

Figure S. Reaction scheme for formation of nitric oxide radicals via oxidation of arginine side chains on proteins.

Production of nitric oxide (NO ), by hydroxylation of arginine, is a part of normal cell signalling. In addition to being a radical, and hence potentially damaging in its own right, nitric oxide can react with superoxide to form peroxynitrite, which in turn decays to yield the more damaging hydroxyl radical. Nitric oxide was first discovered as the endothelium-derived relaxation factor, and this loss of nitric oxide by reaction with superoxide may be an important factor in the development of hypertension. 

Barker, J.R., Lohr, L.L., Shroll, R.M., Reading, S. Modeling the organic nitrate yields in the reaction of alkyl peroxy radicals with nitric oxide. 2. Reaction simulations. Phys. Chem. A 107, 7434-7444 (2003)... 

Sherwood AG, Gunning HE (1963) Reactions of unsaturated Ixee radicals with nitric oxide. Radical-induced scission of caibon-triple bonds. J Am Chem Soc 85(21) 3506-3508... 

An important side reaction in all free-radical nitrations is reaction 10, in which unstable alkyl nitrites are formed (eq. 10). They decompose to form nitric oxide and alkoxy radicals (eq. 11) which form oxygenated compounds and low molecular weight alkyl radicals which can form low molecular weight nitroparaffins by reactions 7 or 9. The oxygenated hydrocarbons often react further to produce even lighter oxygenated products, carbon oxides, and water. 

Physical properties of hexachloroethane are Hsted in Table 11. Hexachloroethane is thermally cracked in the gaseous phase at 400—500°C to give tetrachloroethylene, carbon tetrachloride, and chlorine (140). The thermal decomposition may occur by means of radical-chain mechanism involving -C,C1 -C1, or CCl radicals. The decomposition is inhibited by traces of nitric oxide. Powdered 2inc reacts violentiy with hexachloroethane in alcohoHc solutions to give the metal chloride and tetrachloroethylene aluminum gives a less violent reaction (141). Hexachloroethane is unreactive with aqueous alkali and acid at moderate temperatures. However, when heated with soHd caustic above 200°C or with alcohoHc alkaHs at 100°C, decomposition to oxaHc acid takes place. 

Radical Reactions with Nitric Oxide and Nitrogen Dioxide... 

Another redox reaction leading to arenediazonium salts was described by Morkov-nik et al. (1988). They showed that the perchlorates of the cation-radicals of 4-A,A-dimethylamino- and 4-morpholinoaniline (2.63) react with gaseous nitric oxide in acetone in a closed vessel. The characteristic red coloration of these cation-radical salts (Michaelis and Granick, 1943) disappears within 20 min., and after addition of ether the diazonium perchlorate is obtained in 84% and 92% yields, respectively. This reaction (Scheme 2-39) is important in the context of the mechanism of diazotization by the classical method (see Sec. 3.1). 

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